1. Field of Invention
The invention relates to an apparatus and method for treating the surface of a microelectronic workpiece, and in particular, an apparatus and method for scanning the microelectronic workpiece through a fluid used to treat an exposed surface of the microelectronic workpiece.
2. Description of Related Art
Advances in microelectronic technology cause integrated circuits (ICs) to be formed on microelectronic workpieces, such as semiconductor substrates, with ever increasing density of active components. The formation of ICs is carried out by sequential application, processing, and selective removal of various materials on the workpiece. And, during formation, the exposed surface of the workpiece requires cleaning steps to periodically remove process residue and debris. Various compositions have been developed for removal of specific classes of materials from substrates in semiconductor substrate processing, including both dry and wet cleaning technologies.
However, more recently, cryogenic aerosols have been developed to remove particulate from workpiece surfaces using momentum transfer from the impinging cryogenic aerosol jet. This dry cleaning application has been particularly useful in semiconductor manufacturing. Cryogens that have been used for removal of particulate contamination include argon, carbon dioxide, and water. In cryogenic aerosols, an aerosol jet is produced containing frozen particles moving at subsonic or supersonic speeds. Therein, the size of the frozen particles depends on the thermodynamic conditions of the jet, including the pressure, temperature, flow, and the particle forming conditions, which depends largely on the initial phase of the material supplied for forming the jet and the nozzle design. As noted above, carbon dioxide and water have been used in certain applications. However, for high purity cleaning in semiconductor manufacturing, the avoidance of surface damage is of great import. Therefore, nitrogen and nitrogen/argon mixtures have been used for semiconductor substrate cleaning.
Although cryogenic aerosols have proved effective in removing particles from contaminated workpieces, a problem has been discovered in the cleaning process whereby particles that have been removed from a substrate at times re-contaminate cleaned surfaces of the workpiece. In particular, it has been discovered that such re-contamination occurs when the aerosol jet impinges on portions of the workpiece table that is scanned through the aerosol jet. Particulate on the upper surface of these portions of the workpiece table are dislodged and, in part, transferred to the workpiece surface. Moreover, particulate on the peripheral edge of the workpiece, as a result of prior handling, may be redistributed to the center of the workpiece using conventional scanning techniques.